Oxygen Reduction Process Research Articles

Ab initio insight into the electrolysis of water on basal and edge (fullerene C20) surfaces of 4 Å single-walled carbon nanotubes.

The extreme surface reactivity of 4 Å single-walled carbon nanotubes (SWCNTs) makes for a very promising catalytic material, however, controlling it experimentally has been found to be challenging. Here, we employ ab initio calculations to investigate the extent of surface reactivity and functionalization of 4 Å SWCNTs. We study the kinetics of water dissociation and adsorption on the surface of 4 Å SWCNTs with three different configurations: armchair (3,3), chiral (4,2) and zigzag (5,0). We reveal that out of three different configurations of 4 Å SWCNTs, the surface of tube (5,0) is the most reactive due to its small HOMO-LUMO gap. The dissociation of 1 H2O molecule into an OH/H pair on the surface of tube (5,0) has an adsorption energy of -0.43 eV and an activation energy barrier of 0.66 eV at 298.15 K in pure aqueous solution, which is less than 10% of the activation energy barrier of the same reaction without the catalyst present. The four steps of H+/e- transfer in the oxygen evolution reaction have also been studied on the surface of tube (5,0). The low overpotential of 0.38 V indicates that tube (5,0) has the highest potential efficiency among all studied carbon-based catalysts. We also reveal that the armchair edge of tube (5,0) is reconstructed into fullerene C20. The dangling bonds on the surface of fullerene C20 result in a more reactive surface than the basal surface of tube (5,0), however the catalytic ability was also inhibited in the later oxygen reduction processes.

Enhanced Inter-Molecular Charge Transfer Mechanism of the N-Doped Graphene/Carbon Nanotube Heterostructure Toward Oxygen Reduction Process for Zn-Air Battery

Enhanced Inter-Molecular Charge Transfer Mechanism of the N-Doped Graphene/Carbon Nanotube Heterostructure Toward Oxygen Reduction Process for Zn-Air Battery

Unveiling the Inter-Molecular Charge Transfer Mechanism of N-Doped Graphene/Carbon Nanotubes Heterostructure Toward Oxygen Reduction Process for Zn-Air Battery

Unveiling the Inter-Molecular Charge Transfer Mechanism of N-Doped Graphene/Carbon Nanotubes Heterostructure Toward Oxygen Reduction Process for Zn-Air Battery

Self-powered electrochemical sensing platform based on zinc-air battery via synergy of the light filtering effect and photoassisted oxygen reduction reaction

Self-powered electrochemical sensor has received widespread attention due to it does not require an external power supply. In this study, a self-powered electrochemical sensor based on visible light assisted zinc-air battery (SPES-ZAB) was used as a feasible platform to identify changes in light intensity, which was developed a concealed sensing strategy to expand the application range of UV-Vis absorption spectroscopy. Typically, the core of the zinc air battery is an oxygen reduction catalyst, of which the realization of the oxygen reduction reaction through photo-assisted catalyst is one of the emerging strategies. In this self-powered system, zinc as anode and the polyterthiophene as photocathode were used to construct zinc-air battery and realize the output voltage of the SPES-ZAB through the regulation of light intensity. In addition, we used rhodamine B, potassium permanganate and dopamine self-oxidation solution as model analyte to study the light filtering effect and the sensing performance of SPES-ZAB. Through the filtering effect of the solution on the light intensity, the photocathode oxygen reduction process can be adjusted to achieve the ability of the SPES-ZAB to detect the target. Compared to the results of UV-Vis absorption spectroscopy, the SPES-ZAB exhibits good linear relationship range and excellent universality in the detection of high-concentration colored solutions. This is the first time the use of SPES-ZAB as sensing platform to detect the target in homogeneous system, which will expand the application range of self-powered sensors.

Engineering the Catalytic Properties of Two-Domain Laccase from Streptomyces griseoflavus Ac-993.

Laccases catalyze the oxidation of substrates with the concomitant reduction of oxygen to water. Recently, we found that polar residues located in tunnels leading to Cu2 and Cu3 ions control oxygen entrance (His 165) and proton transport (Arg 240) of two-domain laccase (2D) from Streptomyces griseoflavus (SgfSL). In this work, we have focused on optimizing the substrate-binding pocket (SBP) of SgfSL while simultaneously adjusting the oxygen reduction process. SgfSL variants with three single (Met199Ala, Met199Gly, and Tyr230Ala) and three double amino acid residues substitutions (Met199Gly/His165Ala, His165Ala/Arg240His, Met199Gly/Arg240His) were constructed, purified, and investigated. Combination of substitutions in the SBP and in the tunnel leading to Cu2 ion (Met199Gly/Arg240His) increased SgfSL catalytic activity towards ABTS by 5-fold, and towards 2.6-DMP by 16-fold. The high activity of the Met199Gly/Arg240His variant can be explained by the combined effect of the SBP geometry optimization (Met199Gly) and increased proton flux via the tunnel leading to Cu2 ion (Arg240His). Moreover, the variant with Met199Gly and His165Ala mutations did not significantly increase SgfSL’s activity, but led to a drastic shift in the optimal pH of 2.6-DMP oxidation. These results indicate that His 165 not only regulates oxygen access, but it also participates in proton transport in 2D laccases.

Enhanced electrochemical advanced oxidation on boride activated carbon: The influences of boron groups

Exploring an efficient electro-catalyst is fundamentally important to enhance degradation of persistent organic pollutants during electrochemical advanced oxidation process. In this work, boride activated carbon (BAC) containing different boron group content was prepared as low-cost and efficient catalysts. BAC possessed a more positive onset potential of oxygen reduction reaction (0.458 V vs. RHE) and a faster rate of H2O2 generation (365 mg/L pH=3), compared with activated carbon (0.425 V vs. RHE, 138 mg/L pH=3). DFT calculations and XPS results revealed that -BC3 and -BC2O active groups enhanced oxygen adsorption, and small electronegativity difference between B and O facilitated the desorption of •OOH. The rate of in-situ phenol degradation (0.193 min−1) increased by an order of magnitude as compared to activated carbon (0.018 min−1), because BAC promoted the in-situ conversion of H2O2 to •OH. Therefore, it provided a theoretical base for the further application of boron catalyst in two-electron oxygen reduction process.

Efficient solar-driven H2O2 synthesis in-situ and sustainable activation to purify water via cascade reaction on ZnIn2S4-based heterojunction

Hydrogen peroxide (H2O2) is a significant green oxidant for environment and new energy, especially for Fenton-like system. Onsite production and sustainable consumption of H2O2 are the two critical challenges. Here, a fantastic 2D/1D hierarchical layered ZnIn2S4/TiO2 heterojunction is reported as an efficient catalyst for in-situ H2O2 production via 2-electrons oxygen reduction (ORR) process and be rapidly activated to high concentration hydroxyl radical (•OH) for water purification under visible light irradiation. The high-quality catalyst enables superior H2O2 production rate of 1530.59 μmol h−1 g−1 with an external quantum efficiency of 10.39% illuminated at 400 nm, is much higher than that of reported photocatalysts. The bimetallic sulfide ZnIn2S4 can effectively promote the activation of H2O2 due to the unsaturation of sulfur atoms, so that the wastewater containing tetracycline (50 ppm) can be degraded by 90% only within 60 min by ZnIn2S4/TiO2via this cascade reaction. This work provides a novel strategy and ZnIn2S4-based catalyst for photocatalytic Fenton-like reaction.

Synergistically catalytic enhanced of Zn–N/Co–N dual active sites as highly efficient and durable bifunctional electrocatalyst for rechargeable zinc-air battery

The theoretical energy density, stability and cost of Zn-air batteries (ZAB) are far inferior to the most advanced lithium-ion batteries due to the irreversibility of zinc electrodes and sluggish electrocatalytic performance of oxygen reduction (ORR) and oxygen evolution (OER) processes. Herein, we designed a simple strategy to fabricate a quaternary Zn–Co–N–S co-doped tubular carbon (0.3-Zn-Co-N/S–C) via direct pyrolysis of various mixtures of precursors. The high porosity of 3D nanostructure not only provides better mass transfer but also offers a large number of active sites thereof superior ORR and OER performances. As a result, the rechargeable ZAB fabricated using optimized 0.3-Zn-Co-N/S–C as cathode exhibited a higher open-circuit voltage, stable discharge rate, and better reversibility, even exceeding the state-of-the-art Pt/C catalyst in alkaline solution. The catalytic mechanism indicates that the synergistic effect of Co metal nanoparticles, Co–N/Zn–N active sites, and the high-yield of N/S-doped tubular carbon dominate the outstanding catalytic performance.

Metal‐Free Electrocatalysts for Oxygen Reduction to Hydrogen Peroxide

Hydrogen peroxide (H2O2), as an environmentally friendly and highly efficient oxidation reagent, is now widely and increasingly used in many areas. The traditional anthraquinone synthesis process, however, is energy and capital intensive with low efficiency. Electrochemically reducing oxygen (O2) to H2O2 with metal‐free catalysts is considered a promising alternative. This work describes the two‐electron oxygen reduction process from both thermodynamic and kinetic aspects and summarizes the designing rules for effective H2O2 formation catalysts. This includes tuning the binding energy of the intermediate species, the concentration of dissociation active sites, and adjusting the dielectric constant of solvents. These principles are successfully applied to the design of various metal‐free catalysts by proper structure engineering and heteroatom doping, which shows both high activity and efficiency. Furthermore, pH and temperature effects are presented with a view toward reaction optimization. An outlook of future challenges is also discussed.

Tuning the Oxygen Vacancy of the SrSc0.175Nb0.025Co0.8O3−δ Cathode toward Enhanced Oxygen Reduction Reaction for H+-SOFCs by Water Uptake

The cell output performance of proton-conducting solid oxide fuel cells (H⁺-SOFCs) is still unsatisfactory due to insufficient intrinsic proton conduction in the traditional perovskite oxides. Previously, we found that the introduction of water can activate proton conduction in the cathode part of the SrSc₀.₁₇₅Nb₀.₀₂₅Co₀.₈O₃₋δ (SSNC) to enhance its oxygen reduction reaction. To explore the mechanism, we conducted a detailed analysis using X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and a distribution of relaxation times. Studies found that the introduction of water reduced the valence of the Co ion, increased more oxygen vacancies for generation of more proton defects, and thereby accelerated the process of oxygen reduction. The rate-limiting step of SSNC cathode for oxygen reduction reaction process was changed from the charge transfer process to the surface exchange and oxygen ion diffusion by water uptake. The research results may bring new progress to the development of H⁺-SOFCs.

Interfacial Co-N bond bridged CoB/g-C3N4 Schottky junction with modulated charge transfer dynamics for highly efficient photocatalytic Staphylococcus aureus inactivation

• CoB/CNs Schottky junction with interfacial Co-N bond was prepared; • CoB/CNs presents excellent performance for photocatalytic S. aureus inactivation; • Interfacial Co-N bond can efficiently modulate the charge transfer dynamics; • Two-step single-electron induced O 2 reduction (O 2 → ·O 2 – → H 2 O 2 ) is enhanced. Interfacial engineering plays a critical role in modulating the electron transfer dynamics of photocatalysis, but has been rarely explored. Herein, a novel cobalt boride/graphitic carbon nitride nanosheet (CoB/CNs) Schottky junction with interfacial Co-N bond was successfully prepared to uncover the function of interfacial chemical bond in photocatalytic antibacterial process. Density functional theory (DFT) calculation and experimental investigation demonstrate that the interfacial Co-N bond can act as an electron transfer channel to efficiently steer the electron transfer from CNs to CoB, and then an upward band bending with the height of 0.26 eV is formed in CoB/CNs Schottky junction. The formed upward band bending can rapidly separate the photogenerated electron-hole pairs by preventing electrons from flowing back to the CNs, which causes the surface electron transfer efficiency ( η trans ) to increases from 41.8% (CNs) to 57.7% (CoB/CNs-2). Rotating disk electrode (RDE) results demonstrate that compared with CNs (n = 2.38), the oxygen reduction reaction in CoB/CNs-2 (n = 2.19) is more selective to a two-electron transfer route. Meanwhile, further research on reactive oxygen species reveals that it is an indirect two-step single-electron oxygen reduction process, which is beneficial for the generation of ·O 2 – and H 2 O 2 . As a result, 7 × 10 7 CFU/mL of Staphylococcus aureus ( S. aureus ) can be completely inactivated by CoB/CNs-2 with 125 min under visible light irradiation. It is expected that our work will provide some guidance for the exploitation of more advanced hybrid photocatalysts system through interfacial engineering.

Dual‐Active Sites Engineering of N‐Doped Hollow Carbon Nanocubes Confining Bimetal Alloys as Bifunctional Oxygen Electrocatalysts for Flexible Metal–Air Batteries

Since the sluggish kinetic process of oxygen reduction (ORR)/evolution (OER) reactions, the design of highly-efficient, robust, and cost-effective catalysts for flexible metal-air batteries is desired but challenging. Herein, bimetallic nanoparticles encapsulated in the N-doped hollow carbon nanocubes (e.g., FeCo-NPs/NC, FeNi-NPs/NC, and CoNi-NPs/NC) are rationally designed via a general heat-treatment strategy of introducing NH3 pyrolysis of dopamine-coated metal-organic frameworks. Impressively, the resultant FeCo-NPs/NC hybrid exhibits superior bifunctional electrocatalytic performance for ORR/OER, manifesting exceptional discharging performance, outstanding lifespan, and prime flexibility for both Zn/Al-air batteries, superior to those of state-of-the-art Pt/C and RuO2 catalysts. X-ray absorption near edge structure and density functional theory indicate that the strong synergy between FeCo alloy and N-doped carbon frameworks has a distinctive activation effect on bimetallic Fe/Co atoms to synchronously modify the electronic structure and afford abundant dual-active Fe/Co-Nx sites, large surface area, high nitrogen doping level, and conductive carbon frameworks to boost the reversible oxygen electrocatalysis. Such N-doped carbon with bimetallic alloy bonds provides new pathways for the rational creation of high-efficiency energy conversion and storage equipment.

Mechanisms of oxygen reduction reaction on B doped FeN 4 G and FeN 4 CNT catalysts for proton‐exchange membrane fuel cells

Density functional theory (DFT) was used to calculate the stability, oxygen reduction reaction (ORR) mechanism and activity of B-doped FeN4CNT (carbon nano-tube [CNT]) and FeN4G (G, graphene). The B-doped catalysts are more stable and active than that of the un-doped, especially for FeN4B2G and FeN4B2CNT. Based on the Mulliken charge and electrostatic potential surface of these catalysts, Fe atom is found to be the most active site for the adsorption of O-contained species. It is shown that their adsorption energies decrease in the range: O > OH > Co-ad OH > OOH > O2 > H2O > H2O2 on these catalysts. H2O2 will be directly dissociated into two co-adsorbed OH* or O* + H2O* instead of H2O2 on the graphene series catalysts, and the process of reaction (H2O2 + * → 2OH*) on the active sites of the CNT series catalysts is strongly exothermic. Hence, desorption of H2O2* into the solution is difficult to proceed during the oxygen reduction process. All the catalysts are expected to promote a single site four electron process through the reaction path of I (O2 → O2* → OOH* → O* → OH* → H2O) except for the catalyst of FeN4CNT. The rate-determining step (RDS) for ORR process on FeN4B2G is the first reduction step (O2* → OOH*), while the RDS is the fourth reduction step (OH* → H2O) for the other catalysts. FeN4B2G exhibits the largest on-set potentials of 0.53 V, which is larger than the on-set potential of un-doped B FeN4G catalyst (0.39 V). In addition, the B-doped FeN4CNT catalyst shows the better activity compared to the un-doped ones.

MnN4 Oxygen Reduction Electrocatalyst: Operando Investigation of Active Sites and High Performance in Zinc–Air Battery

AbstractThe development of inexpensive and highly efficient nonprecious metal catalysts to substitute Pt in the alkaline oxygen reduction reaction is an appealing idea in the energy field. Herein, a Mn oxygen reduction electrocatalyst with a half‐wave potential (E1/2) as high as 0.910 V under an alkaline oxygen reduction reaction process is developed, and the dynamic atomic structure change of the highly efficient Mn single‐atomic site is investigated using operando X‐ray absorption spectroscopy. These results demonstrate that the low‐valence MnL+N4 is the active site during the oxygen reduction process. Density functional theory reveals that facile electron transfer from MnL+N4 to adsorbed *OH species plays a key role in the excellent electrocatalytic performance. Moreover, when assembled as the cathode in a zinc–air battery, this MnN4 material shows high power density and excellent durability, demonstrating its promising potential to substitute the Pt catalyst in practical devices.

Tuning oxygen reduction activity on chromia surface via alloying: a DFT study.

Economical electro-catalysts for the oxygen reduction reaction (ORR) are highly desirable for a range of advance energy storage technologies. Chromium compounds have been suggested as one possible source of non-precious metal based catalysts for oxygen reduction reaction (ORR), especially chromia (Cr2 O3 ) which is the most stable form of Cr oxide at room temperature. Using density functional theory+U calculations, we investigate the 4-electron ORR on the hydroxylated Cr2 O3 surfaces alloyed with 17 different transition metals. On the one hand, we find that the ORR overpotential is lower when the Cr2 O3 surface alloyed with elements towards the end of both the first and second rows of transition metals. Among these elements, Cd alloyed Cr2 O3 surface is found to promote the ORR the most, but due to its high toxicity and price it loses out to Zn as the recommended alloyant. On the other hand, we find that the ORR overpotential is generally higher and less varied on the Cr2 O3 surface alloyed with the early-to-mid row transition metal elements (e. g. Zr, Ti). As Cr2 O3 is also a major component in the passive film on stainless steels, where a low ORR rate is desirable to reduce the impact of localized corrosion. This implies that alloying with early-to-mid row transition elements could be beneficial to stainless steels. The difference in oxygen reduction activity is attributed to the tendency of forming stable ORR intermediates during the oxygen reduction process.

КІНЕТИКА СУМІЩЕНИХ КАТОДНИХ ПРОЦЕСІВ У ВОДНОМУ РОЗЧИНІ NaCl

Investigation of the kinetics of combined cathode processes in the electrochemical synthesis of sodium hypochlorite. Intensification of the process of molecular oxygen reduction in aqueous NaCl solution to improve the electrochemical synthesis of sodium hypochlorite using a gas diffusion cathode. Investigation of the effect of the gas diffusion regime on the kinetics of cathode processes, determination of the ranges of potentials and current densities of combined cathode reactions. Cyclic voltammetry for the study of kinetic parameters of the cathode process using the MTech PGP-550M pulse potentiostat. Iodometric titration to determine the concentration of sodium hypochlorite. ranges of potentials of combined cathode processes in conditions without air supply and with air supply through a gas diffusion electrode the possibility of depolarization by air oxygen of the cathode process using the gas diffusion mode of operation of a porous graphite electrode is shown. total and partial reductions (oxygen reduction and hydrogen evolution) polarization dependences without air supply and with air supply in an aqueous solution of 3 mol/dm3 NaCl are constructed to better understand the effect of air supply on the course of combined cathode processes. The obtained polarization dependences prove that the air supply to the gas diffusion electrode leads to an increase in the limiting density of the oxygen reduction current from 2 to 8 mA/cm2, which indicates the prospect of using a gas-diffusion cathode. Changing the nature of the cathode process can significantly reduce the difference in electrode potentials, and by controlling the oxygen supply rate, ClO– can be impeded to the cathode surface. For the field of electrochemical production, it consists in improving the electrochemical synthesis of sodium hypochlorite by increasing the current efficiency and reducing specific electricity consumption. By changing the nature of the cathode process of hydrogen evolution for the reduction of oxygen brought to the cathode-electrolyte interface using a gas diffusion cathode, the problem of cathode reduction of ClО– will be solved without contamination of the final solutions of sodium hypochlorite.

Interplay of the functional units of a binder in the oxygen reduction process of zinc-air battery

Zinc-air battery (ZAB) technology is a strong competitor in the automobile sector for powering automotive. Alas, there are a few issues that restrain them from being commercialized. One prominent issue which has not been discoursed thus far in alkaline ZAB is the impact of the type and content of the binder. The present work incorporates a study conducted to get insights on the impact of eleven different polymeric binders in the air electrode of an alkaline zinc-air battery. They include anion and cation conducting polymers, hydrophilic and hydrophobic polymers. The galvanostatic polarisation curves reveal a huge variation depending on the type of binder. Fumion ionomer, an anion conducting material, shows the highest current density of about 163 mA cm−2 at 0.6 V owing to the right proportion of hydrophilic-hydrophobic segments and ion-conducting nature. A specific capacity of 770 mA h g−1 was obtained when Fumion was employed as a binder with 1 mgPt cm−2. Eventually, the upshot of the experiment motivated us to try a home-made less commonly known anionic binder, functionalised-Polystyrene-Block-Poly(ethylene-ran-butylene)-Block-Polystyrene, which performed on par with Nafion™ and Fumion at a practical operating voltage of ∼1.2 V.

Anti-corrosive mechanism of poly (N-ethylaniline)/sodium silicate electrochemical composites for copper: Correlated experimental and in-silico studies

Poly (N-ethylaniline) (PNEA) composites with varying silicate content were fabricated on copper through a novel electropolymerized strategy in acidic solution. Thickness, compactness, conductivity and adhesive strength of the composite (PNEA-10Si) were optimized as silicate content reached 10 mM. Electrochemical, morphological and solution analyses were employed to evaluate the protective performance of PNEA and PNEA-10Si coatings for copper in 3.5 % NaCl solution. Results of electrochemical analyses indicated that as-prepared coatings retarded the oxygen reduction process efficiently for copper in 3.5 % NaCl solution, drained corrosion current density and elevated interfacial charge transfer resistance. Due to favorable barrier effect, compact structure and low porosity index, PNEA-10Si composite exhibited superior anti-corrosive performance, which was more tolerant than PNEA during long-time immersion. PNEA-10Si coated sample exhibited a stable topography after 144 h immersion with the minimum concentration of released ions revealing the improved protection capacity. Electronic/atomic-multiscale calculations were conducted to clarify the deposition and protection mechanism of as-prepared coatings. Outcomes of density functional theory corroborated that silicate is stabilized in the PNEA layer via electrostatic force; and immobile silicate positively contributed to the charge transfer barrier of the composite. Molecular dynamics simulations evidenced that the favorable compatibility between PNEA and silicate facilitated polymer deposition and confined in-situ ions diffusion.

Химический и электрохимический вклады в редокс-сорбцию кислорода из водына зернистых слоях медьсодержащих нанокомпозитов

Наночастицы металлов в пористых полимерных матрицах проявляют выраженные сорбцион-ные и окислительно-восстановительные свойства. На этих свойствах металл-полимерных нанокомпо-зитов (НК) основан процесс глубокой деоксигенации воды. Ранее обнаружен существенный вклад электрохимической составляющей процесса восстановления кислорода на тонком катодно поляризу-емом зернистом слое медьсодержащего НК. В начальный период процесс лимитируется стадией внешней диффузии кислорода к поверхности гранул НК. В последующем отмечен все возрастающий со временем вклад химической составляющей, характерной особенностью которой является лимити-рование процесса внутридиффузионной стадией переноса кислорода к наночастицам меди и затрата электричества на электровосстановление оксидов металла. Однако при переходе от тонких пленок и слоев к зернистым слоям НК колоночного типа с распределенными по высоте кинетическими пара-метрами вопрос о соотношении вкладов электрохимического и химического маршрутов требует спе-циального рассмотрения.В настоящей работе исследован процесс редокс-сорбции кислорода из воды на динамических зернистых слоях нанокомпозитов медь-сульфокатионообменник (КУ-23, Lewatit K2620) при различ-ных силах поляризующего тока, оценены вклады химической и электрохимической составляющих общего процесса в стационарный период.Найдено, что количество поглощенного кислорода находится в экстремальной зависимости от силы поляризующего тока в допредельном режиме поляризации. Отмечено образование продуктов окисления металлических наночастиц в виде островковых кластеров, часть зерен окисляется с воз-никновением границ оксидных слоев, одинаковых по высоте зернистого слоя. С увеличением высоты зернистого слоя и силы поляризующего тока в допредельном режиме процесс поглощения кислорода становится все более квазистационарным. Показано, что вклады химического и электрохимического маршрутов восстановления кислорода соизмеримы при длительном процессе (100 ч). Часть кислорода поглощается за счет реакции электровосстановления на частицах меди в основном на поверхности зерен нанокомпозита, а часть – за счет автокаталитической химической реакции кислорода с электро-регенерируемыми наночастицами металла в объеме зерен нанокомпозита. Тот или иной механизм более вероятен в зависимости от состояния системы и силы воздействия на нее электрического тока. За счет постоянной электрогенерации ионов водорода и электрорегенерации наночастиц меди, необ-ходимых для восстановления кислорода, устанавливается стационарный режим редокс-сорбции кис-лорода их воды

Oxygen Reduction Assisted by the Concert of Redox Activity and Proton Relay in a Cu(II) Complex.

A copper complex, [Cu(dpaq)](ClO4) (1), of a monoanionic pentadentate amidate ligand (dpaq) has been isolated and characterized to study its efficacy toward electrocatalytic reduction of oxygen in neutral aqueous medium. The Cu(II) mononuclear complex, poised in a distorted trigonal bipyramidal structure, reduces oxygen at an onset potential of 0.50 V vs RHE. Kinetics study by hydrodynamic voltammetry and chronoamperometry suggests a stepwise mechanism for sequential reduction of O2 to H2O2 to H2O at a single-site Cu-catalyst. The foot-of-the-wave analysis records a turnover frequency of 5.65 × 102 s-1. At pH 7.0, complex 1 undergoes a quasi-reversible mixed metal-ligand-based reduction and triggers the reduction of dioxygen to water. Electrochemical studies in tandem with quantum chemical investigation, conducted at different redox states, portray the active participation of ligand in completing the process of proton-coupled electron transfer internally. The protonated carboxamido moiety acts as a proton relay, while the quinoline-based orbital supplies the necessary redox equivalent for the conversion of complex 1 to Cu(II)-hydroperoxo species. Thus, a suitable combination of redox non-innocence and proton shuttling functionality in the ligand makes it an effective electron-proton-transfer mediator and subsequently assists the process of oxygen reduction.